Help Please - A2 2000 Battery Drain, Fuses 36 & 42 - Central Locking

Mophim

Member
Hello. The title contains a lot but I think it's all connected. My question is below my 'quick' explanation.

My battery drains in a day or so. I've checked current battery but also replaced the battery, just to be sure. Both do the same.

I read this post>>
http://www.a2oc.net/forum/showthrea...in-in-4-days-how-to-trace&p=178352#post178352
which mentions the fuses which seem to be giving me problems (36 & 42) and the same symptoms - high amps when locked. Remove these two fuses and it drops.


Following the great fuse guide by Sarge >> http://www.a2oc.net/forum/showthread.php?10712-Fuse-box-Fuses-Fuse-Ratings-Fuse-Locations
it says:
36 - Heated Rear Window Relay 10A
Convenience System Control Unit
Control & Display unit for Air Conditioner/Climate
Tank Filler Flap Release Switch
Additional Heating Button (ECON)

42 - Convenience System Central Control Unit 10A
Anti-theft Alarm Ultra-sonic Sensor

So, then reading another post in the same thread as above:

http://www.a2oc.net/forum/showthrea...in-in-4-days-how-to-trace&p=186930#post186930

suggests the Convenience System Central Control Unit.
With the fuses in, disconnecting this doesn't seem to make the same difference.
I see, looking on ebay, that there are similar units in the OS & NS doors.

My question(s) ... finally
Do both the NS & OS units do the same thing or is the OS one the main unit?
If so, could this problem be the NS side?
I have the drivers door card off but not the NS door card. I don't want to remove it if I don't have to.
The part number of the OS unit is 8Z2 959 802

Thanks in advance

edit: reading another thread, there is talk of the comfort control module under the NS floor. I was getting confused with that and the module in the door. How do I check both?
 
Last edited:
bl**dy Hell!!

I've removed the CCCU unit to try and see if this stops the battery going flat. All seemed OK
However, on a test run earlier, the battery light came on the dash (it's never come on before, despite the other numerous warning lights) and the car was running really rubbish. However, I heard a small click whilst driving, like a relay, the battery light went out and the running suddenly improved.

Any ideas what this could be. What might have 'clicked' or cut in to improve things.

I'm seriously thinking of selling this on. I've never had a 'modern' car with so many faults. It's only got 80,000 on the clock!!
 
Hello. Just an update on this issue as well as one for another thread that was related ( http://www.a2oc.net/forum/showthrea...-Alarm-light-on-door-flashing-when-not-locked )
Sorry for repeating myself and crossing threads but I think it's relevant.

After totally removing the CCCU unit from under the passenger side footwell (to try and resolve the battery draining issue) the alarm light (top of the drivers door) was constantly flashing even though the car wasn't locked and the battery was still draining.

I discovered 2 things:
1. I reconnected the CCCU and that stopped the alarm light flashing.
2. During my initial tests on the battery drain, I checked the battery voltage as well as the alternator voltage. These were initially both fine. However, after disconnecting the CCCU I assumed both battery & alternator were still fine so didn't check again.
However, I decided to recheck and discovered that I'd blown the voltage regulator (on the alternator), probably whilst doing earlier tests, meaning the alternator was no longer charging the battery. This is why, after removing the CCCU, I was still having problems which didn't fit my previous diagnosis.

£13 later and a new voltage regulator was fitted, charging was back to normal and battery was fine.
Also, I tapped the CCCU gentle before refitting as I've had sticking relays in the past (this car has been sat a while before we bought it)
Basically, after doing all this, the battery no longer drains, locked or unlocked, so looks like problems is solved (hopefully for good)

I think the voltage regulator got damaged as a result of accidentally starting the car with the battery terminal not on properly when I was continually checking voltage & amps.
So, my main advice is - Don't run the car with the battery disconnected as this will probably fry the voltage regulator.

Phew!!
 
What do you think was actually causing the battery drain though?

It sounds like the voltage regulator was damaged through your testing of the drain - not causing the drain itself, so I don't understand how replacing this resolved the initial problem?
 
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